The concept of converging plasma jets about a common axis, for example an axis along which reactant is injected into the plasma jets was probably first disclosed in the Japanese laid open application 61-1986-230300 having an application date of Apr. 5, 1985 by Fukanuma, which discloses a plurality of discrete plasma forming guns arranged in encircling relationship about the reactant injection tube so that the plasma jets issuing from these torches are directed by plasma passages arranged at circumferentially symmetrically space locations about the injection tube to converge onto the reactant stream issuing from the reactant injection tube. This system was, it is believed, found to be ineffective and was eventually abandoned.
The first commercially acceptable system, that is commercially effectively being operated is disclosed in U.S. Pat. No. 5,008,511 issued Apr. 16, 1991, to Ross. In this system, a plurality of plasma guns are arranged in symmetrical relationship about a common axis along which reactant is injected through a reactant pipe. The pipe passes through a common anode and is uniformly contacted by the plasma jets in an area of convergence of the jets extending along a plasma jet passage. This system has been found to work effectively and over reasonably long periods of time without significant detrimental effects.
Marantiz et al. in U.S. Pat. No. 4,982,067 issued Jan. 1, 1991 and U.s. Pat. No. 5,144,110 issued Sep. 1, 1992, describe a converging system for converging a plurality of arc currents into a single plasma column and converging them symmetrically onto a stream of reactant issuing along an axis about which the torches and passages are symmetrically arranged.
The recent U.S. Pat. No. 5,298,835 to Muehlberger et al. issued Mar. 29, 1994 describes a converging plasma jet system wherein the plasma outputs of the torches each is directed axially from the respective torches through a passage. These passages converge to direct plasma gas jets issuing therefrom to converge onto a reactant stream issuing from a central reactant tube about which the passages and torches are symmetrically arranged.
One of the inherent problems in all of these systems is to ensure that the reactant stream is uniformly contacted and distributed in the plasma stream formed from the converging discrete plasma jets. Another common problem in some of the systems is spitting (periodic burst of released reactant that built up in the system) which occurs when some of the reactant solidifies within the body of the converging system or block and is periodically dispersed into the plasma stream so that the flow of reactant is non-uniform.